title: Glucose uptake and its effect on gene expression in prochlorococcus.
abstract: The marine cyanobacteria Prochlorococcus have been considered photoautotrophic microorganisms, although the utilization of exogenous sugars has never been specifically addressed in them. We studied glucose uptake in different high irradiance- and low irradiance-adapted Prochlorococcus strains, as well as the effect of glucose addition on the expression of several glucose-related genes. Glucose uptake was measured by adding radiolabelled glucose to Prochlorococcus cultures, followed by flow cytometry coupled with cell sorting in order to separate Prochlorococcus cells from bacterial contaminants. Sorted cells were recovered by filtration and their radioactivity measured. The expression, after glucose addition, of several genes (involved in glucose metabolism, and in nitrogen assimilation and its regulation) was determined in the low irradiance-adapted Prochlorococcus SS120 strain by semi-quantitative real time RT-PCR, using the rnpB gene as internal control. Our results demonstrate for the first time that the Prochlorococcus strains studied in this work take up glucose at significant rates even at concentrations close to those found in the oceans, and also exclude the possibility of this uptake being carried out by eventual bacterial contaminants, since only Prochlorococcus cells were used for radioactivity measurements. Besides, we show that the expression of a number of genes involved in glucose utilization (namely zwf, gnd and dld, encoding glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and lactate dehydrogenase, respectively) is strongly increased upon glucose addition to cultures of the SS120 strain. This fact, taken together with the magnitude of the glucose uptake, clearly indicates the physiological importance of the phenomenon. Given the significant contribution of Prochlorococcus to the global primary production, these findings have strong implications for the understanding of the phytoplankton role in the carbon cycle in nature. Besides, the ability of assimilating carbon molecules could provide additional hints to comprehend the ecological success of Prochlorococcus.
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Edificio Severo Ochoa, Campus de Rabanales, Universidad de Córdoba, Córdoba, Spain.
authors.forename: Guadalupe
authors.initials: G
authors.lastname: Gómez-Baena
authors.forename: Antonio
authors.initials: A
authors.lastname: López-Lozano
authors.forename: Jorge
authors.initials: J
authors.lastname: Gil-Martínez
authors.forename: José Manuel
authors.initials: JM
authors.lastname: Lucena
authors.forename: Jesús
authors.initials: J
authors.lastname: Diez
authors.forename: Pedro
authors.initials: P
authors.lastname: Candau
authors.forename: Jose Manuel
authors.initials: JM
authors.lastname: García-Fernández
mesh_terms: D002250:Carbon Radioisotopes; D000458:Cyanobacteria; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D005947:Glucose / Q000378:metabolism* / Q000494:pharmacology; D005954:Glucosephosphate Dehydrogenase / Q000235:genetics; D007770:L-Lactate Dehydrogenase / Q000235:genetics; D008027:Light; D053858:Metabolic Networks and Pathways / Q000235:genetics*; D010734:Phosphogluconate Dehydrogenase / Q000235:genetics; D048929:Prochlorococcus / Q000235:genetics / Q000378:metabolism*
chemical_list: D002250:Carbon Radioisotopes; D007770:L-Lactate Dehydrogenase; D010734:Phosphogluconate Dehydrogenase; D005954:Glucosephosphate Dehydrogenase; D005947:Glucose